Distillation of hydrocarbon oils



Aug. 17, 1937.

R. E. WILSON DISTILLATION OF HYDROCARBON OILS Filed Dec. 31, 1928 2 Sheets-Sheet l Patented Aug, 17, 1937 UNITE STATES 2,090,245 DISTILLATION F nrnaocmaon 011s Robert E. Wilson, Chicago, 111., assignor to Standard Oil Company, Whiting, Ind., a corporation of Indiana Application December 31,

4 Claims.

The present invention relates to improvements in the art of hydrocarbon oil distillation and is p rticularly directed tomethods for' producing a maximum yield of cleanpressure-still charging stocks from the heavier portions of crude oil and at moderate cost. By clean charging stock is meant a stock which, on cracking by bulk pressure distillation or other cracking operation, does not form any considerable portion of coke.

There are two general methods of producing reasonably clean charging stock from the heavier portions of crude oil. The first is ordinary coking distillation in direct fired batch stills, which gives a high yield of good clean stock, but is expensive to operate, both fuel and labor costs being very high. Practically the whole distillate, except a little gasoline formed by cracking and a'little still wax which comes over near the end of the coking operation; can be used in charging stock for bulk pressure distillation processes without giving excessive coke deposit.

The other'general method of obtaining charging stocks from the heavier portions of crude oil is a non-cracking distillation effected with the aid of steam or vacuum which assists in carrying over the heavier distillates. While the lighter lubricating distillates thus produced make good charging stock, the very heavy distillates for'm excessive amounts of coke in cracking. Thus,

| a skimmed Mid-Continent 'crude oil from which 40 to 45% of gasoline and kerosene have been recovered may be distilled with steam or vacuum to a 78% bottom of very heavy asphalt. Down to about-% bottom the distillate is a very clean stock. From 25% to 15% the distillate is a fair ,cracking stock if mixed with lighter stock. The distillate given off below a 15% bottom is a rather dirty cracking stock and needs to be mixed with large quantities of clean charging stock to enable 0 it to be heavily cracked without excessive coke formation' By this process-it is possible to obtain only between 40 and of clean charging stock from Mid-Continent crude oil, as compared with between and by the coking operr, ation.

Again, if Mid-Continent crude oil is distilled with steam down to a low bottom'in order to distill oi! the heavy lubricants, the bottom is practically worthless for most cracking oper- 0 ations, and'if distilled to coke in an ordinary coking still the amount charged must be very small, and the expense isexcessive.

. By the present process, it is possible to obtain from either skimmed crude or heavy reduced drill: a maximum yield of clean charging stock with the nature of the crude under treatment and the proportions of lubricant products reconvenient source of hot heavy residue from 1928, Serial No. 329,419

at minimum cost, with the production of certain quantities of coke and gasoline as by-products of value. Furthermore, this process is capable of substantially reducing the amount of coke formed in the coking process heretofore employed, particularly if the oil is first reduced to a relatively small residue, for example about 7 to 10% on the original crude oil.

In carrying out the present invention, the crude oil is subjected to non-cracking distillation to produce a heavy residue, which may be highly viscous or substantially solid at ordinary temperatures. This residue is substantially free from oils in the gas oil range as well as lower boiling oils" This initial distillation may be effected batch-wise or continuously, and wholly or in part with steam or vacuum to prevent substantial cracking. The extent to which the non-cracking distillation is carried may bev varied in accordance quired for market conditions. Thus, in the case of an average Mid-Continent pipe line crude, the non-cracking distillation is suitably carried to such an extent that the. residue is not more than about 25% of the crude and in general not less than 7 or 8% in the latter case being of an asphalt-like nature and having a melting point of to F.

The further. treatment 'of this residuum material in accordance with the present invention will be fully understood from the following description' in conjunction with the accompanying drawings, in which I Figure 1 is a diagrammatic view of an apparatus suitable for eflecting the complete distillation of such residues; and Fig. 2 is an elevational view on a larger scale of a suitable form of distillation chamber.

Referring to the accompanying drawings, a fire and steam still Ill, which is the last of a series of continuous. stills, is shown as the source of hot petroleum residue. The source may, h'owever, be the flash drum of a pipe still, or other crude oil, which has preferably been subjected to but little cracking 'or decomposition. The residue passes by pipe II to a pump. In case of dimculty in pumping the hot residue, a cooler I3 is provided for the purpose .of' slightly reducing its temperature to a point at which satisfactory positive pumping may be effected. The pipe II is provided with a valve l4 and a valved pipe l5 leads into the pipe ll between the valve l4 and the pump it. v

The outlet E of the pump it leads into a, able pipe still, shown diagrammatically. at il in which most of the heat is preferably supplied by radiation. The outlet ill of the coil leads into 5 a plurality of manifolds I 8, suitably three in number, each of which is connected by valved pipes I9 with one of the chambers 23. The chambers 23 are of substantial dimensions, and are intended to contain the heated oil while disl0 tillation to coke takes place. The chambers 23 are preferably vertical and are provided attheir upper ends with valved pipes 2| which open to the atmosphere. A valved vapor pipe 22 which communicates with the upper ends of the chambers 23 by valved connections, leads into the base of a suitable fractionating column 23, provided with a so that the vapors, or a part thereof, formed in one chamber may be passed through another empty chamber thereby preheating it for-the reception of residue to be distilled to coke.

The chambers 23 are mounted in an elevated position on suitable supporting structures 3|- which permit access to their lower ends where the chambers are provided with removable closures 32. The closures 32 are: provided with valved 35 pipes 33 for the supply of air or other fluid into the chamber. The pipes 13, associated with each chamber 23, communicate thereinto at various levels thereof. The lowest pipe I! is preferably removably coupled to the pipe 33 so that 40 the heated residue can be supplied into the base of the chamber 23.

The closure 32 may be provided with a small manhole 34, if desired.

The fractionating column 23 may suitably be of the bubble plate type. It is provided with suitable means (not shown) for supplying reflux or condensing vapors to serve as reflux. From the base of the column 23 leads a valved conduit 33, which is provided with a pump 33 and valved 50, branches 3'! and 33 connecting with the inlet and outlet, respectively, of the pipe still l'l, so that a controlled amount of the heaviest condensate,

together with any entrained tar may be returned to the chamber 23. A valved outlet 33 leads from the column 23 at a somewhat elevated point, for

example, above the second or third plate, for the purpose of withdrawing clean charging stock.

The operation is as follows: One of the chambers 23 must first be brought to an elevated tem- 30 vperature so that it will not cool the heated residue below cracking temperature. The heating of the chamber may be effected in any suitable manner. For example, it may be heated by passing steam or water through pipes i3 and I3 into the pipe still I! and passing the highly superheated steam thereinto by pipe l3, the associated manifold I3 and one or more of the associated pipes l3. It has been found that even better results can be obtained by supplying an oil, such as gas oil, in a similar manner, the vapors therefrom passing by pipe 22 to the condenser "where they are condensed. 1

Another method of preheating the chamber 23 is by combustion therein. In preheating by this method the valve in pipe 2| is opened and those in pipe 22 and in the connecting pipe 2'3 are closed. Compressed air is supplied by pipe 33. Any suitable combustible material, for example gas, may be supplied into the chamber and ignited in any suitable manner. Care must be taken to prevent local overheating of the walls, or the formation of an explosive mixture within the chamber. Also, moderately hot products of combustion from any suitablev furnace, such as a portable chamber, maybe introduced through the pipe 33 or other suitable point of entry such as the manhole 34.

In practice, it is preferred to use the chambers 23 in succession or rotation and to pass the vapors produced in one chamber, or a part thereof, by pipes "and 33 into the chamber next to be used and thereby preheat the latter. After passing through the empty chamber, the vapors pass by pipe 22 to the column 23 and condenser 25 associated therewith' No claim is made herein for this method of preheating one chamber by vapors produced in another, or for the structural features whereby such method is effected, the same being described and claimed in the application of Ernest W. Thiele, Serial No. 332,541, filed January 14, 1 929, which has matured into Patent No. 1,947,319, Feb. 13, 1934.

The chamber 23 having been brought to a satisfactory temperature, for example 650 F., or preferably higher, petroleum residue, preferably at a high temperature, is supplied by pump l2 to the pipe still l1, through which it is forced at suflicient speed to prevent excessive cracking or coke deposition in the pipes. A little steam may be introduced to speed the flow through part or all of this preheater system, and thus minimize cracking therein, but this is usually not necessary,

except for the heaviest residues. In passing.

through the pipe-still, the temperature of the residue is raised to a satisfactory temperature,

for example about 900 F., or such a high temperature that asatisfactory coking temperature is maintained in the'chamber 23. It has been found in practice that with heavy residues from Mid-Continent crude the temperaturegof the entering oil must be above 870 F. to insure the production of a reasonably satisfactory coke without too much volatile matter, whiletemperatures above 940? F. tend to cause excessive coke formation in the tubes.

The highly heated residuum is admitted into the chamber 23 by means of one or more of the pipes I3, and builds up from the bottom, coking by its contained heat -until the chamber is substantially full. It is preferred to supply the heated residuum by the lowest pipe I3 as long as possible and then if it begins to clog, to transfer ,the stream successively to the next higher pipe l3. This expedient aids materially in the production of denser coke. As indicated above, it is preferred to pass some or all of the vapors from the chamber 23 in which distillation is being conducted, by means of pipes 23, I3- and I3 into the chamber 23,-next to be used. The vapors pass from the latter chamber 23 by pipe 22 into the fractionating column 23. The fractionating column is supplied with refiuxor cooling medium in suitable amount to yield an over.-

head of gasoline or pressure distillate, which is condensed in the condenser 23. I The condensate collects in the receiver 23, from which it is drawn oil at suitable intervals. The gas and uncon- .densed vapors escape by. pipe 23 and pass to suitable means (not shown) for the recovery of the gasoline therein.

Clean cracking stock is withdrawn by the pipe 39. The reflux from the lowest two or three plates is not sufiiciently cleanand is preferably returned by pipe 35 to either the inlet or outlet of the pipe still l'l.

. It is preferred to maintain the chambers 20 at approximately atmospheric pressure. Accordingly, the pressure applied by the pump 12 is sufficient to force the residue through the pipe still I1 at the desired rate. The destructive distillation may be effected, however, at moder ately super-atmospheric pressures, if desired.

The invention will be more readily understood from the following specific examples of opera- 15 tions on a small commercial scale:

Example I .-Mid-Contine.nt crude is run to a bottom of about 25% by volume in continuous stills and is withdrawn at the rate of about barrels an hour from the last still Ill. The 20 residuum is cooled to 720 F. in the cooler [3, since dimculties are experienced in pumping it at higher temperatures. The residuum is pumped through the pipe-still H, which has eighty-seven tubes of two inches diameter, each approximately fourteen feet long. The outlet temperature is 910 F. The residuum thus preheated is introduced into one of the chambers 20 which has been preheated as described above, and is maintained at substantially atmospheric pressure. .The operation is conducted in the manner described above until the chamber 20 is nearly filled with coke. The yields of products expressed in percentages by weight on the crude. oil are as follows: I

Dry gas 1.37 Gasoline 3.98 Clean charging stock 19.55 Coke 3.01

40 The coke is slightly more porou than ordinary tower still coke and can be readily removed by hand tools or other suitable means after the bottom 32 is removed, or through the manhole 34.

Example II.-Mid-Con'tinent crude reduced under substantially non-cracking conditions to about an 8% residue (by volume) is processed in substantially the same way. The yields of products expressed in percentages by weight on the crude oil are as follows:

Dry gas 0.58

Gasoline 1.37 Clean charging stock 5.65 Coke a- 2.25

After long continuous runs under the conditions described, the tubes of the pipe-still were substantially free from coke deposit.

It may be noted that the amount of coke produced from the complete distillation of residue in the manner described-is substantially less than that produced in tower stills, particularly when the oil is reduced to a low percentage bottom, for example 8%, in still I0.

Although the invention has been described in connection with thedetails 'of specific examples,

it is not intended that such details shall be regarded as limitative of thescope of the invention, except in so far as included in the accompanying claims. H

What I regard as new, and desire to secure by Letters Patent is:

1. The method of decomposing heavy hydrocarbon oils substantially free from constituents of the nature of gas oil and lower-boiling con- 75 stituents to produce a clean condensate charging stock of the character of gasoil and coke, which comprises heating a confined stream of such oil in an elongated zone of restricted'cross-section without the addition thereto'of anysubstantial amount of constituents of the nature of gas oil or lower-boiling oil to a decomposing temperature while causing said stream to move at a sufficiently high speed to avoid substantial deposition of coke in said heating zone, transferring the heated products to an enlarged preheated coking zone without any substantial loss of heat, collecting a body of liquid products of said heating in said enlarged zone without substantial drop inpressure thereon and maintaining said body under low pressure approximating atmospheric at a coking temperature substantially entirely by the heat imparted to said stream of residue in said heating zone for sufiicient time to decompose and reduce unvaporized constituents thereof to coke substantially free from liquid ingredients while removing therefrom only vaporous products. I

2. The method of decomposing heavy hydrocarbon oils substantially free from constituents of the nature of gas oil and lower-boiling constituents to produce a clean condensate charging stock of the character of gas oil and coke, which comprises heating a confined stream of suchoil in an elongated zone of restricted cross-section without the addition thereto of any substantial amount of constituents of the nature of gas oil or lower boiling oil to a temperature between 870 and 940 F. while causing said stream to move at a sufficiently high speed to avoid substantial-deposition of coke in said heating zone, transferring the heated products to an enlarged preheated coking zone without any substantial loss of heat, collecting a body of liquid products of said heating in said enlargedzone without substantial drop in pressure thereon and maintaining said body under low pressure approximating atmospheric at a coking temperature substantially entirely by the heat imparted to said stream of residue in said-heating zone for suflicient time to decompose and reduce unvaporized cbnstituents thereof to coke substantially free from liquid ingredients while removing therefrom only vaporous products.

3. The method of decomposing heavy hydrocarbon oils substantially free from constituents of the nature of gas oil and lower-boiling constituents-to produce a clean condensate charging.

stock of. the character of gas oil andv coke, which comprises heating a confined stream of such oil in an elongated zone of restricted cross-section without the addition thereto of any substantial amount of. constituents of the nature of gas oil or lower-boiling oil to a decomposing temperature while causing said stream to move at a sufliciently high speed to avoid substantial deposition of coke in said heating zone, transferring the heated products to an enlarged preheated coking zone without any substantial loss of heat, collecting a body of liquid products of said heating in said enlarged zone without substantial drop in pressure thereon and maintaining said body under low pressure approximating atmospheric at a coking temperature substantially entirely by the heat imparted to said stream of residue in said heating zone for suflicient time to decompose and reduce unvaporized constituents thereof to coke substantially free from liquid ingredients while removing therefrom only vaporouis. products, cooling the removed vaporous products'to condense therefrom constituents heavier than Bill gasoline while permitting gasoline constituents to remain uncondensed, separately removing from the cooling'operation a minor proportion of condensed constituents heavier than gas oil and containing entrained tarry matter and a major proportion of condensed gas oil constituents tree from entrained. tarry matter, the latter constitu'ting a clean gas-oil charging stock, and returning the heavier condensed constituents contain- ;ing entrained tarry matter to the stream of tion theretoioi any substantial amount of constituents oi the nature of gas oil or lower-boiling oil to a decomposing temperature, while causing saidstream to move at a sufllciently high speed to avoid substantial deposition of coke in said heating zone, transferring the heated products to an enlarged preheated coking zone without any substantial loss 01' heat, collecting a. body 01' liquid products of said heating in said enlarged zone without substantial drop in pressure thereon and maintaining 'said body under low pressure approximating atmospheric at a coking temperature substantially entirely by the heat imparted to said streamoi' residue in said heating zone for sufllcient time to decompose and reduce unvaporized constituents thereof to coke substantially free from liquid ingredients while removing therefrom only vaporous products.

ROBERT E. WILSON. 

